Connecting metal elements and products thereof

ABSTRACT

A method of connecting metal elements by a resistance welding process to produce a high strength joint and particularly to connect a refractory type pre-formed carbide head to a shank of a dental bur formed from steel, and the product formed by such method.

United States Patent Kroder CONNECTING METAL ELEMENTS AND PRODUCTSTHEREOF (72] lava-nor: Eric! A. Km, Hellam. Pa.

[73] Asaignoe: my llesurch I: W Corp Wilmington. Del.

[22] Filed: 1-: 29, 1970 [2|] Appl. No.: 50,444

[52] US. 48. 08/226 1 in" A61: 3102 [58] all sq-u "40x. 126, 238, 239.32/48. 59

[56] macs Chad UNITED STATES PATENTS 2.334.755 21/1243 Eglinton "32/4851 June 20, 1972 2.708.853 5ll95$ MacLcan ..408/238 X FOREIGN PATENTS ORAPPLICATIONS 659.359 10/1951 Great Britain ..32/59 Pn'nwy Bummer-FrancisS. Husa: Auomey--C. Hem: Just ABSTRACTAmbodofconnectingmemldememsbylresistanoeweldingpmecampmdweahighstmngthjoimandpanicuhdylooonnectamfiactorytypeplc-formedcarbideheadtoashankofadentalburformedfi'omswelnnddaeproductfomwdby sudlmalnd.

sununman PHTENTEDJUNZO m2 3579 155 FIG? F|G.8

INVENTOR. ERNEST A. KRODER FIG.6 BY

ATTORNEY CONNECTING METAL EIMNTS AND PRODUCTS THEREOF BACKGROUND OF THEINVENTION Thepresenlinventiominthebroadsemeflsdirectedtotiiebunjoiningoftwopiecesofmetalormetallicsubstancesbya resistance heatingmethod and, in particular, a weldingprocestofonnahighstrengthjointbetweenthesameAtypicalexampleofmchnvopiecesofmetalormetallicsubstancescomprisesapre-formed carbide element,suchasthetiporheadofadentalburcornpriingaselectedmetzlliccarbide formed a,powler-rrieiallurgy technlqua. and theshankofadentalburfonnedfromeithercarbonorstainles steel.

ltiswellknovmthatcuttingheadsofvariomtypescanbeformedbymoldingmetnlliccarbidepowdermaterialbycompresingthesameinamoldandsinteringthepartidestofmnastableconfiguntion.$irnilariy.itiscommonpractioeto forxntheshan'xsofbursirom comentloaai carbon):stahleslsteelbyappropriatemachiningopenmCertain technlquesforoonnectingsuch pre-fonned carbideheadsortipstosteelslunkstoformdentalbtushavebeenproposedheretoformsuchssetforth below.zndover which improve mentsnredesirable=ipTkEififli=aiWic2fi33cufiinghadsofdentalbmstosteelshanheomprisesthesubjectmauerofU.S.PatNo.2,334.755.intbenameofdinton.Dificultyhasbeenexperienced,however.inregardtoeffectingahighsuengthjointbetweentherefractorytypemrbidggflfinghudsandsudlsleelshanksgkwgrbgggilnsaidaforementionedpatengithzbeenproposedtoutikizebnzingmzrerialbetweenafrusto-conicaltippreparedontheendofashmkofadentxlburwhichistobeconnectedtothepre-formedcarbideheadandaeonicalcavitymoldedinsaidheadflnzingmaleriaLsuchassilversoldenispheedwithinthecavirybetweentbetenniaalendoftheshmkofthedentalburandtheinnerrnostportiouofthecrxicalcavityformedinthecarbideheatLWhenheatedtoatempentureadequatetofmethebrafingmsteriaLthetheerydescribedinthepetentisthatthebrazingmetzlwillflowbetweentheadjacentabuttingsurfacesofthepreparedendoftheshankofthedentalburandthecavitywithinthepre-formedcarbideheaWhenthebradngmaterialhasbeenmeltedbyplacingthemernblyinafumacethemoltenmterialflowsintothespaeesbetveentheendoftheshankoftheburandthecavityinthecarbidemwhfleleavinglvoidofappreciables'zeandvolumeintheinnemmendofthecmicalcavitywithinthecarbideMAeeordingly.onl3/partofareaswhicheouldbebrazednogetherareuflized Anothertedmiquewhiehhsbeenmedinthefonnariouofdeatalbushereroforehaeorsktedofprefonningacarbidetipintheformofacylindricalshgforenmandbtmweldingooeendd'thesametoaflatarrbeeexmendingtrmverselywtheusoftbeflunkofacarboasteelbunupongfindingtheflutesiathecarbideheatsaidflutesaboareformedintheeadofthesteelshmkwhichisweldedtothecarbideheetLTominiminenstingthestedslmLpriortoweldingusnlly'splaedwithehmmimnorthelikeflowever,thegrindingofthefltuesirtothe'eldedemlofdtestedslnnkexpouestheseeeloftheshankuponbeingsubjectedtomoistnresuehezpoeedportionsofthestedshmktendmrustandth'nisundcinbleFuthenthehighheatgenentedattheinter'hceoflhectrbideheadaadbursharkcamesthelowermeltingpointwflerialsmmeltandboodorfinetothehighermelthgpointmner'nhvberebythewengthclthemltingjointislproductoftheareaofthejointmdfipliedbythejoimstrengthTheheatgeneratedalsotendstoannealthesteel shank.

SUMMARYOFTHEINVENTIONltistheprincipalobjectot'thepresentinventiontoprovide ble between apre-formed blank, for example, of refractory type metal such as ametallic carbide. lnd a steel shank which is to support said blank. byresistance welding.

It is another object of the invention to provide a high strengthjoimbetween the aforementioned elements while am playing a lower totalamount of heat than has been necessary heretofore A further object ofthe invention is to provide a high strength weldedjoint between acarbide pellet and the steel shank to form the basic assembly ofacarbide-tipped bur for dental purposes Stillanotherobjedoftheinventionstoprovide amethod of correc ing a refractczytype cable: bur to a steelsupportingshanltbynnirnprovedweldingtechniqueresultinginthefonnationofaweldedunionbetweenthenwomembersoffargeaterstrengthincornparisonwiththetotal areaot'the weldrnent tlnn hasbeen pedble heretofore.

Another object of the invention is to providecomplementaryoonicalshapednlrfaeesontherefractorycarbideelement and the:teal slur-.2. referred is above. 2:: paw-id: scifccmcring of themembers incident to being welded together andtherebyproduceaeonoenu'icprodamaswellxprovide means by which aweldmentofeven thickness and fullycoextensiwwiththeadjacemmrfacesoftheshankandcarbide element is produced.

05 3e fez-5571's; are-. c-:' ale: as areasotherobjectsthereoflaresetforthin thefollowingspecification 1ndillustrated on the accompanying drawing cornprising a part thereof.

DESCRlPTlON OF THE DRAWING FIG 1 is a fragmentary vertical sectionalview of m exemplaryrefractorytypemetal element embodyingtheprindplesoftheinvention.

HG. 1A is a slightly enlarged end view of the elements shovminFlGl.

FlGl'tsafngmentzrysideelevationofanexemplaryendconfigu'ationofamemllicmembertobeconnectedtotherefrwytypemetallicelementslnwninm. l.

FIGI-Aisanendvievofthemembershowninflfil.

FIG. 3 is a fragmentary, partially sectioned. foreshortenedsideelevationalviewoftheelementsofHGSlandZmotmtedincontactwitheachother.

FlGJisafngnentary. partially sectionedmideelevnion oftheelernentsshowninFlG.JattheeompletionofthesameFlG.5isafngmentzysideelevation.panlyinseetion,ofa prepm'edendofametallicelementhzvingadifl'erentembodimentofoomiectingmeansfromtlutshowuinm.lappliedtooneendthereofi FlG.6isasubetnntiallyenlzrgednemplarysectiorulviewshowing a reproduction of a of the [in]wddnmtbywhichthecuttinglmdiscormectedtolhetipoftheshmkandthowingthesubstantiallyuniformthicknesof theweldment.

FIGS. 7and8. respecti ely. arealongitudinally sectionedviewandanendvievofafurtherembodimentofeonfiguratiouofcavityfortherdnctorytypemetalelementshovninthepreeedhigfigure.

DESGUFUONOFIHEPREFERREDEMBODIMDFTSThepresmtinveationpertaimtoamethodofconnecting metallic elementstogether by resistance welding, and the produds resulting therefrom. toproduce welded joint ofinventieniapplicabletotheeomiectingofvariomtypesofmetallicelememsandmbstanemandespeciallyarefractorytypernetdloanitemdmoreeonventionalmaterialmchascarbonorstainlesssteelmheinventionespeciallylendsiaelftotheproductionofirnprovedcuttingandlorgrindingtookstillmorespeeiallyJhemethodishigblysuitabktoproduoedentalajointoffargreaterstrengththanhasheretoforebeenpossibmsofsuperiorooncenuicityandstrength,betweenametalliecarbide cut ing tip and a steel shank connected thereto, than has beenpossible heretofore.

Accordingly, without specific limitation thereto, a dental bur has beenselected as an exemplary product which may be manufactured by the methodcomprising the present invention, said invention also including theresulting product. With the foregoing in mind, the characteristics ofthe selected dental bur and the method of forming the same in accordancewith the principles of the present invention are described as follows:

Referring to FIG. 1, a refractory type metallic element 10, whichspecifically compr'ses a cutting tip or head, is illustrated therein.Specifically, the cutting tip or head shown in the figure compraes acylindricai blank formed of metallic carbide and having a conical recesin one end which is coaxial therewith. Various other types and shapes ofcutting and/or grinding tips or heads for other purposes may be formedby the same technique and employ the present invention to form aresulting product.

Incident to forming the cutting tip or head 10, such as by theaforementioned powder-metaiiurgy technique, a cortical aw ty 12 isformed in one end thereof, the axis of the cavity being preciselycoaxial with the head 10. As illustrated in FIG. I. the cavity walksubtend an angle of approximately 90 or 9!. Said angle, however,primarily is illustrative rather than restrictive. Nevertheless, it habeen found that this exemplary angle is satisfactory for the intendedpurpose hereinafter. As in the manufacture of conventional proceses forforming cutting tools. and especially those of small dimensions,thecuttingtiporhead lkforrnedinitiallyasacylindrical blank and flutes orother formations are ground into the daired surfaces thereof tnpl'lfidljlfe c tting or grinding edges after connecting the head to oneend of the shank.

An exemplary supporting shank 14 which is to be connected tothecuttingtiporhead l0isilhtstratedinI-1G.2.Suchshank may, for example,be formed from either carbon steel or Stainles steel. or any otherappropriate metal or alloy. ln accordance with the principles of thepresent invention, it is preferred that said shank be formed from ametal having a lower melting point than the composition of thepreferably refractory metal cutting tip or head 10. The erminal end ofthe shank I4 is provided with a conical tip 16, said conicaltipbeingcoaxialwith theshankandoppositesurfacesthereof preferably subtend aslightly smaller angle than that of the conical cavity for recess 12 inhead 10. The exemplary angleof87isillustratedinl-1Q2butthesamealsoistobere age! v'msril 5 "hm-6 A. iaced-t i s practical for the intended purposes.

Referring to FIGS. 1 and 1A, a pair of exemplary welding electrodes" areillustrated in diametrical opposition to eachotherandthesameengageoppositesidesoftheexemplary cutting head [0. InFIG. IA, it will be seen that the electrodes have concave faces 20 whichcomprise supporting and positioning surfaces which preferably arecomplementary to the sidewallsoftheheadIOwhichareengagedbysaidelectrodes. Thus,theelecu'odesservethedualpurpmeofsupportingand positioningtheheadMaswelladireco'ngcurrenttothehead 10 during the welding operationdescribed hereinafter.

in F165. 2and2A,anotherpairofweldingelecn-odes22areshownindiametricaloppositiontoeachodierandinengagementwithsidesoftheshanklk'lheelecu'odesnaboare provided with concave faces 24 which are complementarypreferablyinallrespectstothesidesoftheshank llwhiehane engage thereby.Said faces. therefore. comprise supporting and positioning surfaces forthe shank incident to connecting theshank lltotheheadloinaccordanoewiththewelding procedure descrflhed hereinafter. Theelectrodes 18 and 22 described hereinabove are formed from conventionalmaterial uu'limd in electrodes employed in electrical resistance eldingtechniqua.

'nteconicaltip lioftheshank .whilenotprcc'selycorm plementary to thecavity or reces 12 of the head 10, neverth les is reasonablycomplementary thereto for practical pun poses. incident to connectingthe 14 to the head 10, the same are aligned by suitable mechanism. notshown, which, for example, supports the pairs of electrodes 18 and 22and effects movement thereof, together with the head 10 and shank 14supported thereby, preferably along a common axis coaxial with said headand shank to move the conical tip 16 into the cavity or reces 12. Thedifference in the angularity of the conical surfaces thereof results invery precise centering of said head 10 in accurate coaxial alignmentwith shank 14.

The aforementioned engagement of the head 10 with the shank 14 isillustrated in exemplary manner in FIG. 3, in which the shank 14 isinterrupted intermediately of i5 ends to foreshorten the view. Themechanism by which the guided movement ofthe head 10 and shank i4 isaccomplished also includes a pushing member 26. shown in fragmentarymanner, by which the shank 14, for example, is moved toward the head 10.Suitable means, represented by the exemplary arrow 28, either moves thehead 10 toward the shank or stabilizes the headagainstmovementawayfromtheshank when the latteris forced toward and into engagement therewith.

After the head it! and shank id have been moved into coaxial alimentwith each other as illustrated in FIG. 3, electric current is applied tothe electrodes 18 and 22, by conventional mechankm, not illustrated, forpurposes of eflecting a high strength welded connection between theexemplary head 10, which comprises a metallic carbide pellet or blank,for exampie, and the steer supporting shank 14'. The a primn'on orwelding current to the electrodes 18 and 22 primarily resultinthelowerrneltingmaterialoftheshank ,suchacarbon steel or stainlesssteel, fusing at least on the surface thereof even though no appreciablefusion of the metallic carbide head 10 may ocoz.

Especially in view of the relatively sharply pointed extremity of theconical tip 16 being in engagement with theinnermostmrfaceportionoftheconicalcavityorreces 12in theheadlmtheouterexu'emityoftheconicaltipwillfusetoa limited depthpractically instaneously, before any remaining portion of the tip 16fuses. Although there is an initially taperedspace betweenthe wallsoftherecess llandeonieal tip l6.prcsureappliedbetweentheheadl0andshank l4forcesthesamefirmlytogetherandresultsin thefmedsurfacematerialoftheextremityofconicaltipldifiusingintothe entire surface ofthe cavity 12 and this phenomenon also deforrrn the conical tip 16suficiently to conform it to the walkofthecaviry12.1heftrsedportionoftip l6isadequate to form an uninterrupted weldmentsurface 30 which, though uniformthicknesthroughouttheentire area of thecoextensivesurfacesoftheconicaltipmandconicalreces 12, thereby providingmaximum poa'ble strength between saidheadandshankbccatsenospacesorgapsexistbetweensaid tipandreces.

Fromtheforegoing, therefore, itwillbeseenthataweldedconnectionuofmaximumstrengthkeflectedbetweentheheadloandshankldbytheweldedconnectionwwhichextendsuniformlybetweentheentire co-engaging surfaceportionsofthemrtialtipwandrecsllduetotheconformingoftheshapeofthetipusothatofrecesIZincidenttoeffectingtheweldment30. Such weldmentalsoisformedwhiletheheadlllandshankuaresupportedbytheelecu'odesmandZZandOtherportionsoftheQuipmenLnotshowminacctnatecoaxialalignmentwitheachothensuchpodtiouingbysaidelectrodesandotherportionsoftbemechanismismaintainedduringandafiertheapplicationofthecurrentTheweldrnent30coolsi1mntlyinviewofthesmallsize0fthebur.atterwhichthedectrodes18and12arereleaedfromtheheadlOandshankltopermitremovalofthefirmlyconncctedheadandshankfmmtheweldingequipment'l'heintegmllyconnectedproductresultingfrom the manufacturing method described above is subjected to furtherfinishingoperationssuchasthegrmdingofflutmuorotherconfiguratiomuponthecuttingtiporheadlilinordertoprovide cuttingedgcsthereon.

A further advantage resulting from the method of manufacturing describedabove. with respect to dental burs in particular. is the fact that. ifdesired. the welded head and shank 14 may be subjected to suitableplating operations to render the shank l4 rust resistant, prior to thegrinding of the surface ofthe head 10 to form the flutes 34 and residingcutting edges thereon. Such grinding of the cutting edges upon the head10 may occur for the full length thereof without contacting the platedsurface of the shank 14. for example. as can be appreciated from FIG. 6.

The resulting product also is precisely concentric and free from anappreciable eccentricity. whereby no final balancing of the product forconcentricity is required. This is important especially in the fonnationof cutting tools operating at high speeds such as dental burs operatingat speeds of 200.000 rpm and upwards. Even the slightest ec .Jicity ofthe burs under such circumstances is highly de'simental to the bearingof dental handpieces in which the burs are used. Concentricity of thecutting head with respect to the supporting shank also is des rabie inother types of cutting tools capable of being formed by the methoddescribed hereinabove for purposes of uniting the cutting head with asupporting shank by welding techniques as described.

The welding action described above occurs by the pasage of current. forexample, from one of the electrodes 18 to one of the electrodes 22.Accordingly. heat initially is generated at the extremity or the ti iii.and due to maximum resistance offered thereby. this causes at km theaforementioncdsurfacefusionofthe cortical tip l6fromtheextremityoutwardly toward the larger diameter of the tip 16. and causesconformity oftip 16 to the surfaceofcavity l2 and also effects theuniform thicknes of weldment 30. Constant pressure exerted upon theshank [4 results in forming the weldment 30 of substantially uniformthickness throughout the entire extent of the coengaging surfacesthereof.

An added advantage of such technique is that such welding action willprevent gmes and from becomingentrappedwithintheweldmentliflandtheprcstn'eexerted between the shank l4and head 10 will insure positive contact between the walls ofthe cavity12 and conical tip 16 at alltimes.'lheconicalshapeoftheweldrnent30alsopro\idesabondedsurfaceofgreaterareabetweenthehead loandshank 14 than inconventionally welded heads and shanks of cutting tools in whichsubstantially flat abutting surfaces are welded together in accordancewith conventional techniqm Accordingly. a welded joint having higherstrength than conventionalcuttingtoolsofsimilartypeisproidcdintheproducts manufactured in accordance with the method describedabove.

lfdesiredtoefl'ectabrazedjoint between thehead l0and shank.suchzbyemployingalowerternperaturethanthe welding tcmpqaturrs utflimedin the method described above. attentionkdirectedtol-IG.Sinwhichitwillbeseenthatthe conicaltip lfiofshanklliseifliercoatedorplaledwithalowermehr'ngmeraloralloythanthacforexamplqfrom whichtheshankllisformeisuchasmpperflheangieofthe conicaltip l6andthatofthecavity[Zinhead IOmaybesubstandally the same a that described above. Byapplying elcc triccun'euttothehad loandshank l4throud'itheusc0felectrodes l8and22.fore.xarnple.asdescribed above.orbyotherw'sesuitablehean'ngthe same.themetalcoafing32 willbesuitablymeltedtoformabrazedconnectionasdistingukhedfromaweldedconnectionbetweensaidheadandshank Whilethepreferrcdshapeofthecavity llinheadloandtipl6ofshankl4isacircularcone.itisalsocontemplared within thepurviewofthe present invention to useadifferentcoufigurarionofstn'facesonthetipmarxltherecesllifdcsircd.ReferringtoFlGS.7and8.itwillbescenthattheexemplaryhead loisproided withareces l2, which. forexample. comprises a square pyramid.Similarly. the tip 16 of shank 14 which is to be connected thereto willbe provided 'th a emen amidal sha but s iightly er an e ta z z ut ofrecess ll fli r-2522x0 51: recess 12 and tip l6 described above withrespect to the recedin embodiments. Otherwise, the welding techniquesdescribed above with respect to the embodiment: shown in HG. 1-4 and 6may be used to connect the head and shank together.

From the foregoing. it will be seen that the present invention providesa relatively simple but highly effective method for connecting metalelemenm together. especially in the cutting tool field and. moreparticularly, in regar to manufacturing dental burs. The utilization ofsubstantially complementary conical surfaces in a cavity in one elementand a tip on another element to be connected to the first elementrtsults in the formation of a more extensive welded area than isafl'orded by flat abutting surfaces which are welded together.

Further, by the utilization ofsmall differences in theangularityofthewnicaltipwithrespecttotheconicalcavi ynr recess. anu'utial fusion ofthe extremity ofthe conical tip will occur in order toconform the tip closely to the shape of the cavity walls and also form aweldrnent which extends from the initially melted tip. outwardly to thefull extent of all surfaces of the cortical cavity in the head memberbeing connected to said tip. Such conical a so flor d accrue: J4-

uf the members with respect to each other to produce preciseconcentricity in the finished product and thereby substantiallyeliminate all necessity of final balancing of such product.

While the invention has been described and illustrated in its severalpreferred embodiments. it should be understood that the invention is notto be limited to the precise de ails hereinillustratedanddescribedsincethesamemybecarriedout in other ways fallingwithin the scope of the invention a illustrated and described.

I claim:

I. A metallic product comprising a metal carbide cutting member havingcutting flutes formed thereon and having a conical cavity surface in onewall thereof. and a metallic shank member of lower fusion temperaturethan said carbide member having a conical end surface initially of aslightly more acute angle than said conical cavity surface. said arbidemember having a greater outer diameter than the portion of the metallicmember upon which said conical end surface is formed and said conicalsurfaces being united by a thin fused layer of substantially uniformthickness of said conical end surface of said metallic member integrallyunited with thecavitymrfaceofsaidcarbidememberandsaidfusedlayerextending continuouslyfrom the inner end of said conical cavitysurfacetothefiillextentinwhichsaidconicalsurfacesare coextensive witheach other.

2.Themetallicproductaccordingtoelaim l in which theangleofsaidconicalerxlsurfaoeinitiallyisnotmorethanj'lThemetallicpr-oduetaccordingtoclairn 1 inwhichlheangleofsaidconiailcavitysurfaceissubstantially andthe angle ofsaidcortical end surface initially being approximatelyJlesthansaidnngleofsaidconicalcavitysurface.

4.!l'aemetallicproductmtiirrgtoclaim linwhichsaid carbide membercompr'ues a sintered powdered metal carbide cutting head member havingflutes formed therein to providecuttingedgesarxisaidmetallicrnemberisasteelshanktosuppoet and matinghead member.

$.lhemetallicproductaccordingtoclaim4inwhichsaidcuttingtoolisdemalbtn'andsaidcarbidememberisofasizeadaptedtobeimedintheoralcavityandsaidsteelshankisof a size adapted to berecei ed within the chuck of a dental handpiece.

0 e e e e

1. A metallic product comprising a metal carbide cutting member havingcutting flutes formed thereon and having a conical cavity surface in onewall thereof, and a metallic shank member of lower fusion temperaturethan said carbide member having a conical end surface initially of aslightly more acute angle than said conical cavity surface, said carbidemember having a greater outer diameter than the portion of the metallicmember upon which said conical end surface is formed and said conicalsurfaces being united by a thin fused layer of substantially uniformthickness of said conical end surface of said metallic member integrallyunited with the cavity surface of said carbide member and said fusedlayer extending continuously from the inner end of said conical cavitysurface to the full extent in which said conical surfaces arecoextensive with each othEr.
 2. The metallic product according to claim1 in which the angle of said conical end surface initially is not morethan 5* smaller than the angle of said conical cavity surface.
 3. Themetallic product according to claim 1 in which the angle of said conicalcavity surface is substantially 90* and the angle of said conical endsurface initially being approximately 3* less than said angle of saidconical cavity surface.
 4. The metallic product according to claim 1 inwhich said carbide member comprises a sintered powdered metal carbidecutting head member having flutes formed therein to provide cuttingedges and said metallic member is a steel shank to support said cuttinghead member.
 5. The metallic product according to claim 4 in which saidcutting tool is dental bur and said carbide member is of a size adaptedto be used in the oral cavity and said steel shank is of a size adaptedto be received within the chuck of a dental handpiece.